JOHANNESBURG (AP) — Former South African president Jacob Zuma staged a walkout Thursday at the commission investigating graft in government during his tenure after failing in his legal bid for the commission's chairman to recuse himself.

Zuma was set to take the witness stand after the ruling, but he left despite appearing under a summons.

Zuma was summoned to respond to questions related to evidence contained in at least 35 affidavits submitted to the commission. But he argued that Deputy Chief Justice Raymond Zondo was biased against him.

Zuma this week appeared before the commission for the first time in more than a year after abandoning his testimony last year.

Zuma’s legal steps against the commission and its chairman are widely seen as delaying tactics to avoid facing questions about his role in alleged corruption that occurred largely from 2009 to 2018.

It is alleged that Zuma allowed the involvement of members of the controversial Gupta family in the appointment of some cabinet ministers. The family now faces U.S. sanctions for alleged activities including using their proximity to Zuma to influence the awarding of lucrative government contracts to companies belonging to the Guptas and Zuma’s son, Duduzane Zuma.

Zuma, who resigned in 2018 under pressure from his African National Congress party, also faces further legal battles with the expected start of his corruption trial in 2021. He is accused of receiving bribes from French arms manufacturer Thales through his former financial adviser Schabir Shaik, who was convicted on related fraud and corruption charges in 2005.